Solenoid valves are suitable for a wide variety of applications and may comprise cartridge valves such as, for example, both direct acting and pilot operated on/off poppet valves.
In one form of a pilot operated poppet valve, a spring acts on an armature to selectively open or close a pilot valve in the center of a poppet depending upon whether the valve is of a normally open or normally closed type. The armature is movable within a solenoid, which includes an energizable coil. When the solenoid coil is energized, the pilot valve is actuated.
A typical prior solenoid coil assembly includes a coil wound on a bobbin and surrounded by a yoke made of a ferromagnetic material. As is well known, the yoke operates to enhance the magnetic conduction or flex density to improve operation. This assembly is encapsulated in a plastic case to retain the same in assembled relation and provide an outer housing. A ferromagnetic washer may also be included in the assembly between one end wall of the case and the yoke. The washer serves the same purpose as the of the housing for connecting to a source of power. One for the plastic case to crack. Specifically, owing to thermal characteristics, the metal yoke expands and contracts at a different rate from the plastic case causing thermal shock which results in cracking of the plastic.
One known solution of the thermal shock problem involves placing the yoke outside of the plastic case. A prior known solenoid assembly includes a plastic case encapsulating a coil and having a top wall, a bottom wall and opposite side walls. One of the end walls has an encapsulated ferromagnetic washer. The top wall is provided with a housing for electrical connectors which are connected to the coil. A metal yoke which is rectangular in configuration has opposite end walls connected by opposite side walls. The yoke is mounted on the plastic casing with its respective end walls and side walls in alignment with the end walls and side walls of the case.
Various valve packages are available which utilize cartridge valves to provide segments of hydraulic circuits ranging from single valves to multi-function manifolds. Such packages can be preassembled and tested for installation in a hydraulic circuit. Particularly, assemblies known as polyhydrons have been utilized to satisfy such requirements. The polyhydron provides interconnections between cartridge valves by drilled holes, thereby eliminating pipe work, expensive fittings and reducing the potential for leakage. Because the valves are mounted closer together pressure losses are reduced and hydraulic circuits become more efficient. The elimination of pipe work results in a neater installation, saving assembly time and wait. Because the package is installed as one complete unit the possibility of introducing contamination of the circuit during assembly is also reduced.
With a polyhydron type valve package it may be necessary to closely mount several cartridge valves. However, access must be provided for electrical connections to the valve solenoids. Thus, with the above-described cartridge valve, including an outer yoke, access must be provided to the top wall mounted housing Further, the outer yoke side walls require that adjacent cartridge valves must be further spaced from one another to allow room for the same, resulting in an increase in the size, and thus weight, of the polyhydron. Also, this type of coil is non-symmetrical, requiring that it be installed on a valve with the end wall having the washer on the side opposite the valve. The reversed installation leads to loss of solenoid power.
The present invention is directed to overcoming one or more of the problems discussed above.